Conventionally, as head chips that deform a driving wall by applying a voltage to the drive electrode formed on the drive walls that segment channels, and that use the pressure generated at that time to eject the ink in the channel from a nozzle, the so called harmonica type head chips are known in which opening parts are provided respectively on the front surface and the back surface.
In such harmonica type head chips, the problem is how to carry out electrical connection between each drive electrode and the drive circuit.
For example, conventionally, an inkjet head has been proposed (Japanese Unexamined Patent Application Publication No. 2004-90374) in which, by providing a penetrating electrode in the cover substrate of the head chip that covers the top part of the channel, the drive electrode inside each channel is brought out to the surface of the cover substrate of the head chip, and the electrical connection between the different drive electrodes and the drive circuit is attempted to be made on the surface of this cover substrate by an FPC, etc., in which the interconnections for driving have been made.
However, providing a penetrating electrode in the cover substrate requires difficult and complicated operations such as, the operation of opening a penetrating hole in the substrate material which is made of a ceramic, etc., and the operation of embedding electrically conductive material inside the penetrating hole, etc. Because of this, an inkjet head has been proposed (Japanese Unexamined Patent Application Publication No. 2006-82396) in which the electrical connections between the different drive electrodes and the drive circuits are made by drawing out and forming, on the back surface of the head chip which is the surface on the side opposite to the surface from which the ink is ejected, connection electrodes that are electrically connected to the different drive electrodes, bonding an interconnection substrate to this back surface of the head chip, and joining an FPC on the edge part of the interconnection substrate.
Forming by drawing out from each channel the interconnection electrodes that are electrically connected to the drive electrodes on the back surface of the head chip in this manner makes it possible to draw out and form the interconnection electrodes easily and also with high accuracy compared to providing penetrating electrodes in the cover substrate, because this can be carried out using the patterning method of the common metal thin films.
However, in the case of a head chip in which higher density is aimed at by providing in parallel two or more rows of channels in a multiple channel construction, since the channel rows are close to one another, it is difficult to draw out the interconnection electrodes up to the edge part of the head chip. For example, in the case of a head chip having two rows of channels, Channel A and Channel B, there is the problem that it is difficult to draw out and form the interconnection electrodes from the channels of row B to the edge part of the head chip on the side that has to go over the channels of row A. This is because it is necessary to go over the channels of row A.
In this case, although it is possible to consider carrying out the patterning so that the interconnection electrodes of the channels of row B are passed between the different channels of row A, there is the problem that it is difficult to carry out patterning so as to pass between very narrow channels, and also, so as not to short with the interconnection electrodes inside the different channels of row A. In particular, if the channels have been placed with a high density and with very narrow pitches, the gap between two neighboring channels is extremely narrow, and it is extremely difficult to pass the interconnection electrodes of the channels of row B between the channels of row A and to bring them out up to the edge part of the head chip without the possibility of short circuits or open circuits.
In FIG. 9 of Japanese Unexamined Patent Application Publication No. 2006-82396, on both surfaces of the interconnection substrate made of a ceramic, etc., and joined to the back surface of the head chip, interconnections are formed that are electrically connected to the different interconnection electrodes formed on the back surface of the head chip, and on each surface of the edge parts of this interconnection substrate are respectively connected FPCs in which are formed the drive interconnections for applying drive signals from the drive circuits.
However, since this operation of connecting these FPCs has to be carried out by placing the head chip with interconnection substrate on a work bench, even if it is easily possible to connect the FPC from the side of the same surface as the surface of joining the head chip with the interconnection substrate, when connecting the FPC from the side opposite to this surface, there is the problem that the head chip becomes an obstruction, it is not possible to place it on the work bench in a stable manner, and the work becomes difficult.
Further, in the case of connecting FPCs respectively on both surfaces, there is the problem that the operation becomes complicated because, after an FPC is connected on one surface, it is necessary to turn the head chip with an interconnection substrate upside down.
In view of this, the purpose of the present invention is to provide an inkjet head in which it is possible to easily carry out the electrical connections of the drive interconnections in order to apply the drive voltages from the drive circuits to each of the channels of two rows that are close to each other in a honeycomb type head chip in which a plurality of rows of channels are provided, which electrical connections are made only at one edge part of the head chip, and also, only on the side of the same surface as the surface of joining with the head chip.